| 摘要 |
A composite filter circuit comprises a first series resonant circuit connected to a single common resistor, resonating at a first frequency, and exhibiting a low-pass filtering characteristic. A parallel resonant circuit includes one circuit element of the first series resonant circuit and resonates at a second frequency. A second series resonant circuit is connected to the single common resistor, resonating at the second frequency, and exhibiting a highpass filtering characteristic. The first series resonant circuit and the parallel resonant circuit constitute a low-pass filter circuit section. This low-pass filtering characteristic results from the total effects of the low-pass filtering characteristic of the first series resonant circuit, a dip characteristic of the parallel resonant circuit, and, in addition, a decreasing characteristic at the second frequency, due to the second series resonant circuit. The second series resonant circuit constitutes a high-pass or band-pass filter circuit section having a high-pass filtering characteristic resulting from the total effect of the high-pass filtering characteristic of the second series resonant circuit and, in addition, the decreasing characteristic at the first frequency due to the first series resonant circuit.
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